Typically the water pumps in cooling systems of an internal combustion engine are driven by a belt. The water pump assembly usually has a shaft which mounts a pump rotor at one end located in the pump chamber and mounts a pulley at the other end exteriorally of the pump chamber. West German Registered Design No. 86-32,771 shows a pulley design for a v-belt or timing belt having a bore so that it can be mounted on the end of a shaft. The pulley is held in place against axial and rotational movement by a press fit.
It has been found that this type of assembly has certain disadvantages and drawbacks. For example, impact-like loads introduced by the belt during operation and the continuous vibrations of the belt have the effect of increasing the torque induced loads on the shaft pulley assembly by reason of the unfavorable relationship between the radius of the rim and the radius of the mounting bore of the pulley. By reason of this, there is the danger that the connection between the two can become loose and under certain extremely adverse conditions, may result in fracture of the hub area of the pulley. This failure can have deleterious consequences. For example, when the cooling system of an internal combustion engine fails without warning, the loosened pulley or broken parts are hurled through the engine compartment or into other moving parts.
Various solutions to this problem have been proposed. For example, the danger noted above in connection with the failure of a cooling system is addressed in French Patent No. 2,230,225. This patent shows a cup-shaped pulley with a rim and a pulley body designed as a single piece with a shaft of the water pump. In order to eliminate the danger of fracture in the transition area between the shaft and the pulley body, a fillet is provided. This necessitates, however, that the support of the shaft in the pump housing or in a pump cover sealing the pump housing needs to be installed underneath the rim to minimize the tipping moment caused by the belt. This means, however, that the seating surface for a roller bearing or the raceways for the rolling elements must be machined into the area of the shaft underneath the rim or as shown in the French Patent No. 2,230,225 in the inside surface of the ring. This type of machining operation is quite tedious and difficult by reason of the fact that the cup-like shape is projecting over the shaft. Consequently the end product is extremely expensive.